While the manufacture and various uses of polyolefin-based fiber, fibrillated film, webs and corresponding nonwoven materials are well known in the textile art, attempts to broadly apply such knowledge to produce products in the area of personal hygiene, such as cover stocks for catamenial devices, disposable diapers, incontinence pads and the like, have met with limited success at best.
In general, such products must have a fluid-absorbent core, usually comprising one or more layers of fluid absorbent material such as wood pulp, rayon, gauze, tissue or the like, and, in some cases, synthetic hydrophilic material such as hydrophilic polyurethane foam.
The fluid-absorbing material is generally provided in the form of a thermally bonded pad, of wood pulp, fiber and conjugate fiber, which may have a rectangular or somewhat oval shape. To protect the clothing or areas around the user from being stained or wetted by fluids absorbed by the pad, it is generally backed by a fluid-impervious barrier sheet. In general, the absorbent product is positioned against the body with the hydrophilic material facing and contacting the body and the fluid impervious barrier layer facing the outside.
To enhance a sense of comfort, such absorbent products also generally employ a facing or cover stock material which covers the body-facing surface of the product. The purpose of this cover is two-fold, namely (1) to structurally contain a loosely packed core of absorbent material as above described and (2) to protect the body from continued direct contact with the wetted absorbent material. The facing or cover stock must, therefore, be very pervious to fluids on the side of the product that is placed against the body, and yet be essentially nonabsorbent, so as to actively promote the immediate transfer of substantially all of the fluid into the absorbent core material with minimal surface fluid retention by the cover stock and minimal lateral migration of fluid along the cover stock surface.
Such material should also feel smooth and soft to the touch. In addition, certain additional characteristics are also sometimes desired, such as visual opacity plus specific coloring and luster on the outer surfaces.
In order to obtain many of above-listed characteristics, however, it is imperative that cover stock utilizing essentially hydrophobic polymeric material, such as polyolefin fiber or film, be made at least temporarily hydrophilic and have the continuing ability to pass aqueous fluids through, even after several insults (i.e. wettings) without wash out or leach out of hydrophilic-promoting agents. This is particularly important in the case of diaper cover stock so as to avoid lateral liquid migration and side leakage without interfering with fabric bonding steps or the wet strength of the final product.
Based on teaching in the paper-making art, it is known that short term hydrophilicity can be imparted to hydrophobic polymers such as polyolefin fiber by using flash evaporation techniques and treating the resulting fiber or filament with hydrophilizing agents such as polyvinyl alcohol or various nitrogen-containing water-soluble polymers (ref. U.S. Pat. Nos. 4,156,628, 4,035,229, 4,082,730, 4,154,647, 4,156,628, 4,035,229, 4,273,892 and 4,578,414).
For personal hygiene purposes, however, the lack of significant resistance to wash out and leaching of art-recognized hydrophilic-promoting additives, plus interference with fiber or web bonding properties under high speed commercial operation, has justified continuing attempts to obtain improved hydrophilic-promoting additives and a longer term wettability. Such efforts include incorporating alkoxylated alkylphenols or corresponding polyoxyalkylenes into spun melt compositions (ref. U.S. Pat. No. 4,578,414). Serious high speed bonding and fluid control problems remain, however.
It is an object of the present invention to more effectively utilize inert hydrophobic polyolefin-containing nonwoven materials in the area of personal hygiene.
It is a further object of the present invention to efficiently utilize polyolefin-containing webs comprised of treated fiber, and/or treated fibrillated film as cover stock.
It is a still further object to obtain and retain hydrophilicity and liquid strike through properties in strong well bonded nonwoven hydrophobic materials such as continuous and/or staple fiber utilizing polyolefin component(s).